The present invention generally relates to reflection liquid crystal display devices, and more particularly to a reflection liquid crystal display device that dispenses with a polarizer.
Recently, reflection liquid crystal display devices have been highlighted because of a demand for power-saving liquid crystal display devices. A power-saving reflection liquid crystal display device that is also downsized and lightweight can be realized by dispensing with a backlight that consumes a large amount of power.
Conventional reflection liquid crystal display devices are classified into the following types: those with two polarizers, those with a single polarizer, and those with no polarizer.
Generally, a two-polarizer reflection liquid crystal display device is defined by a liquid crystal display panel having a liquid crystal, electrodes, and substrates all sandwiched between first and second polarizers, and a reflector provided outside the liquid crystal display panel. A light incident on the first polarizer without the reflector passes through the substrates and a liquid crystal layer to be reflected back from the reflector. The reflected light again passes through the substrates and the liquid crystal layer to be emitted out from the reflection liquid crystal display device through the first polarizer without the reflector. In this case, the incident light passes through each of the first and second polarizers twice. Therefore, the light incident on the reflection liquid crystal display device passes through the first and second polarizers four times in total before being emitted out from the reflection liquid crystal display device.
A single-polarizer reflection liquid crystal display device has the polarizer on the side of a light source, and a reflector sandwiched between a first substrate and a liquid crystal layer. A light incident on the polarizer passes through a second substrate and the liquid crystal layer to be reflected back from the reflector. The reflected light again passes through the liquid crystal layer and the second substrate to be emitted out from the reflection liquid crystal display device through the polarizer. In this case, the incident light passes through the polarizer twice.
A conventional no-polarizer reflection liquid crystal display device includes a guest-host liquid crystal in which a liquid crystal is mixed with a dichroic dye. Some of liquid crystal panels employing a guest-host liquid crystal have two layers of guest-host liquid crystals in mutually perpendicular orientations, and others have a guest-host liquid crystal disposed in a spiral state.
However, the two-polarizer reflection liquid crystal display device has a very low reflectivity with respect to the incident light, and accordingly, a very low liquid crystal display brightness since the incident light passes through the first and second polarizers four times in total before being emitted out from the reflection liquid crystal display device. Further, the two-polarizer reflection liquid crystal display device has the second polarizer and one of the substrates sandwiched by the liquid crystal layer and the reflector, so that the liquid crystal layer and the reflector are separated by the width of the one of the substrate. Therefore, liquid crystal display may be doubled in the two-polarizer reflection liquid crystal display device.
The single-polarizer reflection liquid crystal display device has the incident light pass through the polarizer twice. Therefore, the single-polarizer reflection liquid crystal display device has a reflectivity with respect to the incident light higher than that of the two-polarizer reflection liquid crystal display device having the incident light pass through the first and second polarizers four times in total. However, the single-polarizer reflection liquid crystal display device is required to include a {fraction (xcex/4)} plate to control the ON-OFF switching of liquid crystal display. This {fraction (xcex/4)} plate disperses the wavelength of the incident light, which makes it difficult for the single-polarizer reflection liquid crystal display device to perform a high-contrast liquid crystal display.
The no-polarizer reflection liquid crystal display device has a reflectivity with respect to the incident light higher than that of the single-polarizer reflection liquid crystal display device. However, in a reflection liquid crystal display device having two layers of guest-host liquid crystals in mutually perpendicular orientations, the two layers of the liquid crystals should be activated simultaneously. Therefore, this reflection liquid crystal display device has difficulty in controllability. On the other hand, in a reflection liquid crystal display device having a guest-host liquid crystal disposed in a spiral state, it is necessary to apply a high voltage to turn on a liquid crystal in a vertical position, while an incident light is scattered in a weakly turned-on part of the liquid crystal. Therefore, it is difficult for this reflection liquid crystal display device to perform a high-contrast liquid crystal display.
It is a general object of the present invention to provide a novel and useful reflection liquid crystal display device in which the above-described disadvantages are eliminated.
A more specific object of the present invention is to provide a reflection liquid crystal display device that obtains high brightness and high contrast without employing a polarizer.
It is yet another object of the present invention to provide a reflection liquid crystal display device including:
a liquid crystal layer;
a transparent insulating layer provided in an optical path of a light incident on the liquid crystal layer, the transparent insulating layer having a refractive index substantially equal to one of refractive indexes for ordinary ray and for extraordinary ray of the liquid crystal layer;
a reflector for reflecting the light passing through the liquid crystal layer and the transparent insulating layer; and
first and second substrates provided on first and second sides of an optical member so as to oppose each other, the optical member being formed of the liquid crystal layer, the transparent insulating layer, and the reflector,
wherein an interface formed between the liquid crystal layer and the transparent insulating layer has a plurality of slant parts of substantially the same shape, the slant parts each having a predetermined inclination with respect to the reflector.
According to the present invention, if the refractive index of the transparent insulating layer is substantially equal to that of the liquid crystal layer, a light incident on the reflection liquid crystal display device along an incident optical path vertical thereto is emitted out to travel in the reverse direction in an emission optical path substantially equal to the incident optical path. On the other hand, if the refractive index of the transparent insulating layer is not equal to that of the liquid crystal layer, a light incident on the reflection liquid crystal display device along an incident optical path vertical thereto is emitted out along an emission optical path different from the incident optical path. Therefore, unlike a conventional liquid crystal display device, the reflection liquid crystal display device of the present invention is allowed to optically modulate an incident light without using a polarizer, and accordingly, to perform a high-brightness display of a high contrast ratio. Further, since the reflection liquid crystal display device of the present invention has high brightness, the reflection liquid crystal display device can be used also as a projection liquid crystal display.